It was originally a poem by Robert Burns and was set to music later. Then the lyrics were updated to reflect a modern English language which opened the floodgates as everybody and their brother thought it fair game to alter. Rather than post that many versions, I'll link you to the wiki page which has several.
http://en.wikipedia.org/wiki/Auld_Lang_SyneTechnically the following is the original and correct. It's also nearly incomprehensible:
Should auld acquaintance be forgot,
And never brought to mind ?
Should auld acquaintance be forgot,
And days o' lang syne ?
CHORUS:
For auld lang syne, my jo,
For auld lang syne,
We’ll tak a cup o’ kindness yet,
For auld lang syne.
And surely ye’ll be your pint-stowp !
And surely I’ll be mine !
And we’ll tak a cup o’ kindness yet,
For auld lang syne.
CHORUS
We twa hae run about the braes,
And pu’d the gowans fine ;
But we’ve wander’d mony a weary foot,
Sin auld lang syne.
CHORUS
We twa hae paidl’d i' the burn,
Frae morning sun till dine ;
But seas between us braid hae roar’d
Sin auld lang syne.
CHORUS
And there’s a hand, my trusty fiere !
And gie's a hand o’ thine !
And we’ll tak a right gude-willy waught,
For auld lang syne.
CHORUS